1. Field of the Invention
The present invention relates to a laser exposure device and an optical axis adjustment method in the laser exposure device that adjust the positional relationship between a light source and a lens system of the exposure device or the positional relationship between laser light that has passed through the lens system and a sensor in an electro photographic type copier or printer that uses laser light to perform exposure to thereby obtain an image.
2. Description of the Related Art
As an electrophotographic type image forming apparatus, there is recently known an apparatus that uses laser light from a laser exposure device using a laser light-emitting element as a light source to exposure a photoconductor to thereby obtain an electrostatic latent image on the photoconductor. The laser exposure device using the laser light-emitting element as a light source includes a lens system for focusing the laser light onto a deflector such as a polygon mirror. The laser light-emitting element and a drive circuit therefor are generally supported by a laser holder, and the lens system is mounted on the lens holder. In the laser exposure device, the positional relationship between the laser light-emitting element and lens system need to be adjusted for their optical axes to be in alignment with each other. Further, in the laser exposure device, the positional adjustment needs to be carried out so that a beam detector (BD) for obtaining horizontal synchronous based on which the write start position of the laser light on the photoconductor is determined is in alignment with the optical axis of the laser light that has passed through the lens system.
Therefore, a mechanism that adjusts the positional relationship between the optical axes of the laser light-emitting element and lens system while freely moving laser and lens holders in X and Y directions is provided in a conventional laser exposure device. That is, a needle mounted on a precision stage which is movable in X and Y directions is used to press the laser holder to the lens holder to scrub the two holders against each other for positional adjustment. After the positional adjustment, while the needle is tightly pressed to the two holders for preventing the holders from being displaced from each other as a screw for fixing the two holders is fastened in a stepwise manner.
Further, another mechanism for positional adjustment is known. In the case where a laser exposure device includes, e.g., three optical devices in an image forming apparatus, the mechanism first fixes the position of the two optical devices and then fixes the position of the residual third optical device to complete the fixation of the positions of all the optical devices. This mechanism is disclosed in, for example, Jpn. Pat. Publication (Kokai) No. 2000-314844.
However, in the former adjustment method, since a screw is fastened in a stepwise manner while confirming that the two holders are not displaced from each other, it takes long time for fixing operation and for the entire positional adjustment. Further, in order to move the two holders with high accuracy by scrubbing them against each other, it is necessary to restrict the movement range as much as possible, so that a through hole for receiving the needle needs to be formed in the laser holder at the position in the vicinity of the laser light-emitting element, which places restraint on the wiring of a drive circuit in the vicinity of the laser light-emitting element.
Therefore, it is desirable to provide a laser exposure device and an optical axis adjustment method in the laser exposure device, capable of preventing the laser holder and lens holder from being displaced from each other or preventing misalignment between the optical axis of the laser light and BD, reducing time for the fixing operation after the positional adjustment, and improving the flexibility of the wiring of the drive circuit in the vicinity of the laser light-emitting element.